Components of an Injection Molding Machine, How Everything Works Together

Components of an Injection Molding Machine, How Everything Works Together

In this comprehensive article, I’ll talk about the machine briefly, the parts of an Injection Molding Machine, and how everything works together. I hope, in the end, everything related to the machine will become plain to you. Let’s get to it.

Injection molding has revolutionized the plastics manufacturing industry. It was first invented to solve the BILLIARD BALL problem in the 19th century. Basically, at that time, these balls were made out of the tusks of African Elephants. That not only devastated the elephant population but also was too expensive.

To solve the problem, John Wesly Hyatt invented the molding machine that can mold celluloid and make plastic billiard balls. It is one of the very prototypes of the Plastic Injection Molding Machine. And this was the birth of Plastic Injection Molding. Nowadays, it’s a go-to machine for mass-producing plastic parts and products.


What is an Injection Molding Machine?

As you already know the basics about this mechanical marvel, I won’t bore you with another definition. But in a non-convectional way, Injection Molding can be defined like this. Melt plastic, inject it into a mold and wait for some time. Voila! You’ve got the desired plastic product.

However, in reality, it’s a complex machine with lots of microdetails. Mainly, it has three parts: The injection unit, the Mold, and the Clamp. Melted plastic pallets go through a hopper inside the injection unit and get to the molding section with the help of a screw. 

The screw works as a plunger as it transports the melted plastics forward aka the mold unit. There it takes the form of the desired product.

I know, it sounds a bit tight-script-ish. But don’t worry, I have a dedicated paragraph about the parts in the later part of the article. There you will get to know about how the machine works briefly.

The Different Parts of the Machine and How Everything Works Together

Parts of the Machine

Well, at this point in the article, you’re already familiar with the three main parts of an injection molding machine. Now, it’s time to know about these briefly. Without further ado, let’s see what I have for you.

Injection Unit

There are mainly three divisions of the injection unit: Hopper, Heated Barrel, and Screw. All three parts work equally and send melted plastic to the next phase of the machine.

At first, the Hopper contains all the plastic pallets aka raw materials. The only job it does that it sends these babies into the heated barrel.

The heated barrel then slowly melts down all the pallets and moves forward. Before the mid-20th century, injection molding machines use to have a plunger for melted-plastic transportation. But there was a problem using just a plunger.

What happened is that plastics conduct heat poorly. As a result, there had been fully melted plastic in the outer layer and semi-melted in the middle. This results in lumps and degrade production. To solve this, engineers introduced the Reciprocating Screw.

It is often regarded as the most vital piece that revolutionized the plastics industry. This necessary upgrade solves the non-melting plastic problem in three ways.

First, it eliminates the middle layer of the melted unit. As a result, the molding unit only gets the evenly distributed heated section.

Second, the screw has flights. It slowly transports the plastic units forward by rotating uniformly. This results in proper mixing, and you get even heat all over the molten part.

Third, the screw itself works as a heater. While rotating, it created friction with the barrel’s wall. Hence, fraction creates heat that keeps the unit in liquid form. And thus, the last part of the injection unit ends.

Mold Unit

A lot of people don’t consider this unit as an independent unit. But if you go back to the very first injection molding machine, you’ll find this as a separate unit. 

The injection unit transfers molten material in this section’s empty space known as the mold cavity. At first, the cavity is filled with air. As soon as molten plastic enters, it releases air via vents. Here the liquid plastic takes the shape of the cavity image.

Clamp Unit

After the plastic solidifies into the desired shape. Now, it’s time to give it the final touch. And the Clamp Unit provides it. This section has two main parts: Clamping Motor Drive and Tie Bars. Mainly the unit is responsible for cooling and removing the manufactured product.

Here, the mold slowly opens several millimeters to alloy the air rush in and minimize the vacuum, and then quickly comes back. At this point, the water flow beneath the unit already solidified the construction. After that, ejector pins push the product and make it ready for packaging.

Well, this is it. This is the most basic form of injection molding. I tried to give you the simplest explanation of the complex machine. I hope, it’ll be helpful for you.

Different Types of Plastic Injection Molding Machines

There are many types of injection molding machines in the world. The division is based on a lot of different factors. I’ll try to give you the names according to all factors. So, let’s get to it.

Drive Method

Depending on the drive method, the machines have three types. They are:

  • Hydraulic Injection Molding Machine
  • All-Electric Injection Molding Machine
  • Hybrid/ Servo-Hybrid Injection Molding Machine 

Trend of Switching Mode

Molding machines divide into two types here. The names are:

  • Vertical Injection Molding Machine
  • Horizontal Injection Molding Machine

Applicable Raw Materials

There are three types of raw materials used in injection molding machines. They are thermoplastic, thermosetting plastic, and powder plastic.

Clamping Structure

There are three types of machines here too.

  • Single-Cylinder/ Double-Cylinder/ Four-Cylinder Direct Pressure Injection Molding Machine
  • Toggle Type Injection Molding Machine
  • Composite Direct Pressure Injection Molding Machine.

Injection Structure

Lastly, the injection structure classification method. The names here are:

  • Monochrome Injection Molding Machine
  • Multi-color Injection Molding Machine

Frequently Asked Questions

How expensive an Injection Molding Machine is?

Answer: There are too many types of these machines. So, it’s hard to spill the right amount for one. However, the price range of an injection molding machine is from 50,000 USD to 200,000 USD. You’ll also need to make a specific facility to use the machine. So, the overall call will add an extra 20 to 30K USD.

Is injection molding cheaper than CNC?

Answer: The answer is not that easy. But in short words, injection molding is much more expensive than CNC. Because in injection molding, you need to mold your parts, and the molding machine is too expensive.

What is the life of an injection mold?

Answer: It certainly depends on how you use and maintain it. However, if maintained correctly, it will last a hundred million of cycles or more. So, the main game is to work properly.


Injection molding is the most common and revenue-making method of plastics mass producing. Since the beginning, the contribution of this machine to the industry is huge. The article was all about the mechanical marvel.

If you’ve gone through the whole article, you will see the different parts of the injection molding machine and how they work together. I’ve also added a section where you’ll see the names of the machine’s different types. Lastly, I wrapped everything up with the most frequently asked questions in the sector. I hope, this article has been helpful to you.

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